The present application is based on Japanese patent application 2000-112340 filed on Apr. 13, 2000, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a construction machine such as a hydraulic excavator. Particularly, the invention relates to a hydraulic control circuit provided in the construction machine.
2. Description of the Background
In the past, where excavation work is carried out by a hydraulic excavator, earth and sand scooped by a bucket are loaded on a dump truck waiting behind the hydraulic excavator by rotating an upper rotating body of the excavator. The operation is carried such that when loading onto the dump truck is terminated, an excavator arm is turned while elevated, and returned to an excavation point.
The conventional hydraulic control circuit is designed so that oil is supplied from a common pump to a control valve for an arm and a control valve for rotating. Because of this, the arm, which has the smaller load, is first operated, so that the rotating operation is delayed.
In this case, an operator has to carry out a complicated operation in which an arm operating lever is operated moderately, to provide sufficient oil pressure for the rotating operation. The complicated operation is difficult to do unless an operator is a skilled person. However, when pulling and rotating of the arm are carried out while adjusting an operating lever, there occurs a problem that rerotating to the excavation point is delayed to lower the work efficiency.
To cope with the foregoing, control has been carried out so that a valve for throttling a quantity of oil discharged from an arm cylinder at the time of an arm pulling operation is provided to overcome the delay of the rotating operation during the arm pulling operation. However, in this hydraulic control circuit, since the valve is provided in a circuit on the rod side of an arm cylinder, even if throttling is done relatively strongly, a sufficient throttling effect could not be a obtained. The digging equipment herein denoted in simplified manner as an xe2x80x9cexcavator arm,xe2x80x9d as a rule comprises an integral single boom or a boom in two parts, plus a shovel stem and an excavating implement.
It is an object of the present invention to provide a construction machine capable of carrying out a rotating operation and an excavator arm operation properly even if both the rotating and the arm pulling are operated simultaneously.
In accordance with at least an aspect of the invention, the above and other objects are addressed by a rotating motor for causing a rotating operation such as a rotating operation of an upper rotating body. The arm operation comprises an operating such as arm pulling and arm-in, wherein xe2x80x9carm-inxe2x80x9d means bringing in the excavator arm. Actuators include an arm cylinder for causing an excavator arm operation. Control valves control supply and discharge of oil between each of hydraulic pumps and each of the actuators. The control valves incline a control valve for a rotating motor and a control valve for an arm cylinder. A switching valve is switched between a first position for separately supplying oil from the hydraulic pumps to the control valve for the rotating motor and the control valve for the arm cylinder, and a second position for uniting and supplying oil from the hydraulic pumps. A detector outputs signals responsive to the rotating operation and the arm pulling operation respectively when those operations are carried out. A switching controller switches the switching valve to the second position when the signals are output substantially simultaneously. A meter-in flow-controller such as meter-in flow-control valve restricts a quantity of oil supplied to the arm cylinder when the switching valve is switched to the second position.
In this case, when rotating and arm pulling are operated simultaneously, signals are respectively output from the detector and applied to the switching controller. The switching controller recognizes that the signals are output simultaneously, and switches the switching valve to the second position. When the switching valve is switched to the second position, oil flows discharged from the plurality of hydraulic pumps are united and supplied to the rotating motor and the arm cylinder through a specific control valve. Accordingly, the quantity of oil supplied to the rotating motor and the arm cylinder is increased. Thereby, the quantity of oil necessary for quickly carrying out the rotating and arm pulling operations is secured.
In this state, the meter-in flow-controller restricts the quantity of oil supplied to the arm cylinder, so that the arm pulling speed can be suppressed. Accordingly, even if the rotating and arm pulling are operated simultaneously, respective operations of the rotating and the arm pulling can be done quickly, the delay of the rotating operation can be overcome, and the rotating and arm pulling operations can be realized properly.
Preferably, the meter-out flow controller is provided for restricting a quantity of oil discharged from the arm cylinder when the switching valve is switched to the second position.
In this case, when the quantity of oil supplied to the arm cylinder is throttled, the meter-out flow controller also simultaneously throttles the quantity of oil from the arm cylinder. Accordingly, cavitation can be prevented when, for example, the arm descends by its own weight without any operation.